Laminates of phenolic resin impregnated cellulosic substrates



United States Patent 3,537,951 LAMINATES OF PHENOLIC RESIN IMPREGNATEDCELLULOSIC SUBSTRATES George J. Anderson, Wilbraham, and Ronald H.Dahms, Springfield, Mass., assignors to Monsanto Company, St. Louis,Mo., a corporation of Delaware No Drawing. Filed July 25, 1968, Ser. No.747,442 Int. Cl. B32b 27/00, 27/10, 27/42 US. Cl. 161-259 7 ClaimsABSTRACT OF THE DISCLOSURE Laminates made from phenolic resinimpregnated cellulosic substrates. The phenolic resin used is made froma substituted phenol and formaldehyde. The substituted phenol is made byreacting a specific mixture of cyclopentadiene codimers. The productlaminates have an improved combination of water absorption, solventresistance, heat resistance, electrical properties, and physicalproperties.

BACKGROUND In the art of making phenolic laminates using cellulosicsubstrate members in a sheet-like form, it has long been appreciatedthat phenol-formaldehyde resins tend to make laminates which, whenimpregnated with sufiicient such resin to have acceptable strength, haverelatively poor water absorption, electrical properties, solventresistance, heat resistance, and physical properties. Unless there is acareful balance of properties in such a product, the laminate is of lowquality at best.

There has now been discovered a new and very useful class of laminatesmade from phenolic resin impregnated.

cellulosic substrates in which the impregnating resin is a certainsubstituted phenol-formaldehyde resole resin. Depending upon the type ofcellulosic substrate employed, and upon the amount and particular typeof such substituted phenol-formaldehyde resin employed, the productthermoset laminates characteristically have an improved combination orbalance of properties, including physical strength properties, waterabsorption, electrical properties, solvent resistance, and heatresistance.

SUMMARY This invention is directed to new and very useful laminates.These laminates employ a plurality of integral cellulosic substratemembers in sheet-like form arranged face to face in deck fashion. Eachsuch substrate member is impregnated with a thermoset substitutedphenolformaldehyde resole resin, and each such member is bonded to itsadjacent member by such thermoset resin in a generally continuous mannerin face-to-face engagement.

The phenol-formaldehyde resole resin employed in the products of thisinvention has a formaldehyde to phenol mol ratio of from about 0.8 to2.0 (preferably from about 0.9 to 1.5), and is produced by reacting inthe presence of a basic (preferably organic) catalyst under liquidaqueous phase conditions a certain substituted phenol mixture withformaldehyde. The resole resin used in this invention further has arelatively high molecular weight as shown by the fact that it issubstantially water insoluble but has a methanol solubility such that a60 weight percent solution thereof can be prepared in methanol. Suchmethanol solution characteristically has a viscosity not greater thanabout 5000 centipoises, and preferably in the range from about 50 to 500centipoises. In addition, this resin has a free formaldehyde contentwhich is less than about weight percent.

3,537,951 Patented Nov. 3, 1970 It will be appreciated that the aldehydeto phenol ratios herein described have reference to the total amount ofphenol present before a reaction, including the phenol which issubstituted.

The substituted phenol mixture used to make such resin is itselfprepared by initially reacting phenol under Friedel- Crafts conditionswith a mixture of cyclopentadiene codimers which comprises (when in aform substantially free of other materials wherein the sum of allcomponent compounds of any given such mixture equals substantially 100weight percent):

(A) From about 50 to 99 weight percent of compounds each molecule ofwhich has:

(1) the dicyclopentadiene nucleus (2) from 10 through 13 carbon atoms(3) as nuclear substitutents from 0 through 3 methyl group, and

(B) From about 1 to 50 weight percent of compounds each molecule ofwhich is a codimer of cyclopentadiene with at least one acyclicconjugated alkadiene having from 4 through 6 carbon atoms per molecule.

In a preferred such mixture, a minor amount of cyclic and/or acyclicconjugated alkadiene is present, typically less than about 15 weightpercent (same basis) and having 5 or 6 carbon atoms per molecule. Thus,such a mixture can comprise:

(A') From about 70 to weight percent of dicyclopentadiene (B) From about10 to 30 weight percent of compounds each molecule of which is a codimerof cyclopentadiene with at least one acyclic conjugated alkadiene havingfrom 4 through 6 carbon atoms per molecule, and

(C') From about 2 to 15 weight percent of compounds each molecule ofwhich is a cyclic or an acyclic conjugated alkadiene having 5 or 6carbon atoms per molecule.

In another preferred such mixture, both a minor amount (less than about10 weight percent-same basis) of compounds containing the indenenucleus, and a minor amount (less than about 15 weight percent-samebasis) of compounds containing the phenyl vinylidene structure arepresent. Thus, such a mixture can comprise:

(A) From about 1.5 to 10 weight percent of compounds each molecule ofwhich has:

(1) the indene nucleus (2) from 9 through 13 carbon atoms (3) as nuclearsubstituents from 0 through 4 methyl groups (8") from about 50 to 70weight percent of compounds each molecule of which has (1) thedicyclopentadiene nucleus .(2) from about 10 through 13 carbon atoms (3)as nuclear substituents from 0 through 3 methyl groups,

(0") from about 4 to 10 weight percent of compounds each molecule ofwhich is a codimer of cyclopentadiene with at least one acyclicconjugated alkadiene having from 4 through 6 carbon atoms per molecule,and

(D) from about 4 to 30 Weight percent of compounds each molecule ofwhich has:

(1) a phenyl group submitted by a vinylidene group,

(2) from 8 through 13 carbon atoms (3) as substituents from 0 through 3groups selected from the class consisting of methyl and ethyl.

In still another preferred such mixture, the-re are controlled, minoramounts (from about 2 to 9 weight percent-same basis) of each ofmethylcyclopentadiene and codimers of cyclopentadiene withacycliconjugated alkadienes relative to a major amount (from about 92 to98 weight peroent-same basis) of dicyclopentadiene. Thus such a mixturecan comprise:

(A"') from about 92 to 97 weight percent of dicyclopent-adiene,

(B"') from about 1 to weight percent of compounds each molecule of whichis a codimer of cyclopen-tadiene with at least one acyclic conjugatedalkadiene having from 4 through 6 carbon atoms per molecule, and

(C"') from about 1 to 4 weight percent of compounds each molecule ofwhich is a codimer of cyclopentadiene with a methylcyclopentadiene;provided that the sum of (A) and (C) in any given such cyclopen-tadienedimer mixture is always at least about 95 weight percent, and preferablyabout 97 weight percent, thereof (same basis).

Preferably, such a mixture contains at least about 3 weight percent.(same basis) of (B).

Examples of suitable such acyclic conjugated alkadienes includebutadiene, piperylene, isoprene, 1,3-hexadiene, 1- methyl 1,3pentadiene, and the like. Examples of suitable such cyclic conjugatedalkadienes include cyclopentadiene, methylcyclopentadienes, and thelike.

At the time when such a mixture is reacted with phenol as indicated,there can be present as diluents inert (e.g. as respects reactivitytowards components of such mixture and phenol under Friedel-Craftsreaction conditions) organic compounds, such as aromatic and aliphatichydrocarbons. While there is no apparent upper limit on the amount ofdiluent which may be present, it is preferred that the amount of diluentpresent range from about 5 to 50 weight percent (same basis).

By the phrase when in a form substantially free of other materialsreference is had to a mixture (e.g. of starting materials, of product,or the like, as the case may be) which is substantially free (e.g. on ananalytical or theoretical basis) substances (like inerts as respectsreactivity with phenol under Friedel-Crafts catalysis) other than suchmixture itself. For example, the afore-indicated starting mixture ofdiene codimers could have an inert hydrocarbon diluent admixed therewithsuch as benzene, lower alkyl substituted benzenes, naphthalenes andalkane hydrocarbons containing from 6 through 10 carbon atoms permolecule.

The term cyclopentadiene as used herein refers to the cyclic compoundhaving the structure:

The term dicyclopentadiene as used herein refers to the cyclic compoundhaving the structure:

I O OH H 2 w/ s 2 C C H Hz The term vinylidene as used herein hasgeneric reference both to vinylidene radicals (CH =C and vinyl radicals(CH =CHorCH=CH-); observe that in carbocyclic compound mixtures used inthis invention having a phenyl group substituted by a vinylidene group,alpha-methyl substitution is included in this definition, as well asstyrene, methyl styrene, and ethyl styrene.

All solids herein are conveniently measured using ASTM Test ProcedureNo. D11555 Such a starting material diene codimer compound mixture canbe prepared synthetically or derived by suitable preparative proceduresfrom naturally occurring crude petroleum, as those skilled in the artwill appreciate. A preferred mixture of such diene codimer compounds foruse in this invention is a petroleum derived blend of components havingdiluents already incorporated thereinto.

Cir

For example, suitable such mixtures are shown in the following TablesI'III. In Table I is shown an example of such a mixture availablecommercially under the trade designation Dicyclopentadiene Concentratefrom the Monsanto Company, St. Louis, M0. in Table II, one availablecommercially under the trade designation Resin Former P from Hess Oiland Chemical Co. of New York, N.Y. and in Table HI, one availablecommercially under the trade designation Dicy-clopentadiene from UnionCarbide Company, New York, N.Y. and also one available commerciallyunder the trade designation Dicyclopentadiene from Eastman KodakCompany, Rochester, N.Y.

C) Conjugated alkadienes (Cyclic and acyclic conjugated alkadienescontaining 5 and 6 carbon atoms per molecule 4 (D) Alkenes: cyclopenteneTotal of (A), (B), (C), and (D) (E) Inert hydrocarbon diluents (total)(1) Benzene (2) Methylpentane, methylcyclopentaue,

and hexane 1 Data in Table I derived from vapor-liquidphasechromatography and mass spectrography.

2 Based on total weight of diene dimer compounds and other componentsincluding diluents.

3 These alkadiencs are usually piperylene and isoprene; composition ofsuch alkadienes is somewhat variable.

4 These alkadienes are usually piperylene, isoprene and cyclopentadiene;composition of such alkadienes is somewhat variable.

5 Diene codimer compound mixture when in a form substantially free ofother materials wherein the sum of all component compounds in any givensuch mixture equals substantially weight percent.

TABLE II Weight percent diene codimer Total weight mixture percentcomponents Component basls 1 only 2 Arylcycloalkenes 1. 7 1. 9

Indene 1. 7 1. 9

Dicyclopentadienes 65. 5 74] Dicyclopentadiene 48. 9 55. 3Methyldicyclopentadiene 15. 2 17. 2 Dimethyldicyclopentadiene 1. 4 1. 6

Cyclopentadiene/alkadiene codimers 8. 0 9. l

Codimers of cyclopentadiene with acyclic conjugated alkadienes havingfrom 4 through 6 carbon atoms per molecule:

Codimer with butadiene- 6. 0 G. 8 Codimer with isoprene 2. 0 2. 3

Arylalkenes 6. 9 7. 7

Styrene 5. 6 6. 3 Alphamethylstyrcne 1. 3 1. 4

Trimers incorporating cyclopentadiene, mcthylcyclopentadiene or conjugated alkadienes having from 4 through 6 carbon atoms per molecule 6. 47. 2

Dione codimer mixture sub-total 88. 5 100. 0

Unidentified Components 2. 1

Inert dilnents Benzene Toluene Xylene and ethylbenzene Naphthalene TABLEIII Union Eastman Carbide, Kodak, wt. wt. Component percent 1 percent lDicyclopentadieues 93. 2 95. 6 Methyldicyclopentadienes 3. 0. 9

Cyclopentadiene/acyclic conjugated diene codimers 2. 1. 9 Heavy ends 0.20. 6 Unidentified 1. 1 1.0

'lhese values derived using a combination of vapor liquid phasechromatography and mass spectrometry.

2 Heavy ends here comprise primarily trimers of such components ascyclopentadiene, methyclopentadiene, and conjugated alkadienescontaining from 4 through 6 carbon atoms per molecule. Typically, theseheavy ends are reactive with phenol under Friedel-Craits conditions astaught herein.

To react phenol with such an aforedescribed cyclopentadiene codimermixture, it is convenient to use Friedel-Crafts conditions, asindicated.

The term Friedel-Crafts conditions as used herein refers to theconventional conditions known to those of ordinary skill in the art usedfor the alkylating or arylating of hydrocarbons (including phenol) bythe catalytic action of aluminum chloride or equivalent catalyst in thepresence of appropriate heat and pressure. Conveniently, the phenol andsuitable Friedel-Crafts acid catalyst are mixed, brought to the propertemperature and the diene codimer compound mixture metered into theacidified (or catalyzed) phenol.

For the purposes of this invention, the reaction of diene codimercompound mixture with phenol is preferably carried out at temperaturesin the range of from about 25 to 200 C., although higher and lowertemperatures can be used. Also, the reaction is preferably conductedunder liquid phase conditions at or below atmospheric pressures althoughsuperatmospheric pressures can be used. Inert hydrocarbons, as indicatedabove, generally facilitate the process. Such inert hydrocarbons can bereadily removed, such as by vacuum stripping, at the completion of thereaction if desired. Especially when stripping is contemplated, thernost preferred inert hydrocarbons having boiling points between about70 and 140 C. The progress of the reaction can be monitored, if desired,by measuring the quantity remaining of unreacted diene codimer compoundusing, for example, vapor phase chromatography.

Friedel-Crafts catalysts which may be used in place of aluminumchloride, or together with aluminum chloride, include:

(A) Other inorganic halides, such as gallium, titanium, antimony andzinc halides (including ZnCI (B) Inorganic acids, such as sulphuric,phosphoric and the hydrogen halides (including HF);

(C) Activated clays, silica gel alumina, and the like;

(D) BF and BE, organic complexes including complexes of BF with organiccompounds, such as ethanol, butanol, glycol, phenol, cresol, anisole,ethyl ether, isopropyl ether, di-n-butyl ether, formic acid, aceticacid, and propionic acid, or with inorganic acids, such as phosphoricacid, sulfuric acid, and the like; and

(E) Alkyl, aryl and aralkyl sulfonic acids, such as ethane-sulfonicacid, benzene sulfonic acid, benzene disulfonic acid, chlorobenzenesulfonic acid, 3,4-dichlorobenzene sulfonic acid, cresol sulfonic acids,phenol sulfonic acids, toluene sulfonic acids, xylene sulfonic acids,octylphenol sulfonic acid, B-naphthalene sulfonic acid,1-naphthol-4-sulfonic acid, and the like.

When BF as such, is employed, it is conveniently fed to a reactionmixture in gaseous form. While any combination of diene codimer compoundstarting mixture, phenol and catalyst can be used, it is particularlyconvenicnt to react for each 100 parts by weight of phenol about 10 to100 by weight parts of such diene codimer compound mixture (on a 100weight percent basis in a form substantially free of other materials) inthe presence of less than about 10 weight percent (based on the phenol)of acid catalyst.

TABLE II Broad range Process variable Preferred range Temperature, CAbout to 200 0..-- About 70 to 125 0.

Reaction time Less than about 4 About 10 to hours. minutes.

Catalyst (based on Less than about 10 About 0.1 to 1.0

p on weight percent. weight percent.

Inert hydrocarbon con- Up to about weight About 2 to 10 weight tent(based on total percent. percent. weight diene codimer compound mixtureand diluent).

Total diene codimer About 10 to 100 parts About 20 to parts compoundmixture by weight. by weight. (based on parts by weight phenol).

1 On a 100 weight percent basis in a form substantially free of othermaterials.

In general, to produce a resole phenol-formaldehyde resin for use inthis invention from a substituted phenol product prepared as justdescribed, such product is neutralized under aqueous liquid phaseconditions as by the addition of base, and then from about 0.8 to 2.0moles of formaldehyde per one mole of (starting phenol is mixed with thesubstituted phenol product (now itself a starting material). Also abasic catalyst material, such as hexamethylenetetramine, ammoniumhydroxide, triethylamine, sodium hydroxide, mixtures thereof, and thelike, is introduced into the reaction mixture. The pH of this reactionmixture using such basic catalyst is maintained about 7.0.

It will be appreciated that the formaldehyde to phenol ratios hereindescribed have reference to the total amount of phenol present before areaction, including the phenol which is substituted by thecyclopentadiene codimer compound mixture, as described above. Aqueousliquid phase preparation conditions are generally but not necessarilyused.

To optimize electrical properties in such resole products it ispreferred to use as a basic catalyst, when reacting such substitutedphenols with formaldehyde, one which is organic (substantiallynon-ionic) in character, such as triethylarnine, or the like. Suitableprocess variables for making such resole are summarized in Table IIIbelow:

The resole product produced by reacting the substituted phenol withaldehyde as described above is one composed of methylolated substitutedphenol which has been methylolated by the formaldehyde to a desiredmethylol content and optionally advanced (e.g. .the molecular weight ofthe methylolated substituted phenol increased) as by heating asnecessary or desirable to make a resole product having characteristicsgenerally as described above. Such a resole can be regarded as being thereaction product of the above-described substituted phenol mixture andformaldehyde under aqueous base catalyzed conditions as described whichproduct can be thermoset by heat alone without the use of a curingcatalyst. In general, however, such resole product as made is a browncolored, unstable, multiphase aqueous emulsion whose viscosity depends,in any given instance, upon process and reactant variables but whichusually ranges from a syrupy liquid to a semi solid state. A resoleproduct derived from such aqueous phase as a brown colored materialwhose viscosity varies from a syrup to a solid. Such emulsion ispreferably dehydrated and formed into a varnish for use in making theimpregnated sheet products of this invention.

Thus, when such emulsion is dehydrated under heat and reduced pressureto a water content generally under about weight percent but over about 2weight percent, there is produced a single-phased, clear, resole resinin the physical form usually of a high solids viscous dark fluid. In anygiven instance, its total solids content (residual) water content, andviscosity depend upon the amount of substituted phenol aldehyde productpresent, the mole ratio of aldehyde to substituted phenol, type andamount of methylolation catalyst, conditions and reactants used tosubstitute the phenol, methylolation temperature, degree of advancement,and the like.

When such a dehydrated liquid resole is further dehydrated to a watercontent under about 2 weight percent, there is prouced a solid,so-called one-stage lump resin which consists substantially of pureresin. Usually the water content after such a dehydration is not lessthan about 0.5 weight percent of the product resin, in general.

Suitable resole dehydration conditions typically involve the use of avacuum ranging from about to 28 inches Hg and temperatures ranging fromabout 40 to 90 C. Higher and lower temperatures and pressures can beemployed, as those skilled in the art appreciated.

To prepare a varnish from a dehydrated resole product as describedabove, such resole is then conveniently dissolved in a relativelyvolatile, inert organic solvent medium having properties generally asdefined above. It is not necessary, and it is preferred not, to preparethe resole resin in the form of a solid before dissolution thereof inorganic solvent. In general, the water content of the partialldehydrated resole material is controlled so that the Water content ofthe solution of resole resin in such solvent medium (the varnish) isbelow about 15 weight percent (based on total weight).

While the organic liquid used has properties as indicated above, it willbe appreciated that such liquid can comprise mixtures of diiferentorganic liquids. Preferred liquids are lower alkanols (such as ethanoland methanol) and lower alkanones (such as acetone or methyl ethylketone). The term lower refers to less than 7 carbon atoms per moleculeas used herein. Aromatic and aliphatic (including cycloaliphatic)hydrocarbons can also be employed as solvents for a given resin,including benzene, toluene, xylene, naphthalene, nonane, octane,petroleum fractions, etc. Preferably, the total Water content of avarnish of the invention is below about 10 Weight percent, and morepreferably falls in the range of from about 0.5 to 5 weight percent.

Those skilled in the art will appreciate that care should preferably betaken when using this procedure to use an organic liquid system in whichthe phenolic resole resins are completely soluble as well as any waterpresent. Adding, for example, a ketone or an ether-ester solvent likebutyl Cellosolve generally improves the water tolerance (ability todissolve water) of a solvent system.

The varnishes thus made typically comprise:

(A) From about 20 to 75 weight percent of the above describedsubstituted phenol-formaldehyde resole resin,

(B) From about 0.5 to 15 weight percent of dissolved water, and

(C) The balance up to 100 weight percent of any given varnish being anorganic liquid which:

(1) is substantially inert (as respects such resin mixture),

(2) boils (evaporates) below about 150 C. at atmospheric pressures,

(3) is a mutual solvent for such resin and for such water (if present).

These varnishes are characteristically dark colored, onephase, clearliquid solutions having a viscosity ranging from about 5 to 5000centipoises, the exact viscosity of a given varnish depending uponchemical process and product variables used in manufacture. Forimpregnating applications, viscosities of from about 50 to 500centipoises are preferred.

The total solids content of a given varnish product can be as high asabout 85 weight percent or even higher and as low as about 20 weightpercent or even lower, but preferred solids contents usually fall in therange of from about 25 to 65 weight percent.

In general, an individual cellulosic substrate used in the laminates ofthe present invention is an integral preformed sheet-like membercomposed substantially of cellulose fibers in a woven, non-woven, ormixed structure. Typical thicknesses range from about 3 to 30 mils(under about 10 being preferred). Such members are well known to the artand include paper and cloth broadly; they need have no specialcharacteristics. The cellulosic fibers used in such a substrate membercan be of natural or synthetic origin and the sheet member can be in awoven or nonwoven state. Typical well known sources for cellulose fibersinclude wood, cotton, and the like. Typically, average cellulosic fibersused in substrates employed in this invention have length to widthratios of at least about 2:1, and preferably about 6:1, with maximumlength to Width ratios being variable.

The term substantially as used herein in reference to cellulose fibershas reference to the fact that substrate comprises mainly cellulosefibers with not more than about 5 to 10 percent of any given cellulosicsubstrate being other components, such as non-fibrous fillers, diluents,and the like, or fibrous non-cellulosic materials, such as those derivedfrom organic sources (e.g. protein, synthetic organic polymeric fiberslike polyesters, etc.) or inorganic sources (e.g. silicious fibers ormetallic fibers). Such other components when and if present,characteristically have size ranges which are not greater in magnitudethan the cellulosic fibers. Preferably such other components are under 1weight percent of the total weight of a starting individual cellulosicsubstrate member.

Particularly when high electrical properties are desired in a productlaminate of the invention, the cellulosic substrate member should have alow ash content. Ash contents under 1 weight percent (based on totalcellulosic substrate member weight) are preferred, and those having ashcontents under 0.5 weight percent are more preferred.

Before a liquid resole resin composition such as described above is usedfor impregnation of a preformed cellulosic substrate (such as describedabove), it is convenient to dilute such composition with an organicliquid (as described above) so that the total solids concentration ofsuch resulting composition typically ranges from about 20 to weightpercent (as indicated), with solids contents of 40 to 80 percent beingpreferred. A primary reason for impregnating with such an organic liquidcontaining composition is to permit one to control the extent ofimpregnation and to impregnate a preformed cellulosic substrate such aspaper without causing a deterioration in the Wet strength thereof. Thus,by using an organic liquid system as described, the wet strength of apreformed cellulosic substrate material after impregnation and beforedrying to remove volatile liquid is maintained at convenient processinglevels for subsequent drying, advancing, etc. by machines, etc.

In general, impregnation of a preformed substrate cellulosic member bysuch a liquid resole composition can be accomplished by any conventionalmeans, including spraying, dipping, coating, or the like, after which itis convenient and preferred to dry the so-treated sheet to removeresidual volatile components and thereby leave a desired impregnatedsheet-like construction. In drying, care is used to prevent leavingexcessive volatile material in the impregnated sheet. In general, avolatile level of less than about 8 percent by weight is desired.

For purpose of this invention, volatile level is conveniently determinedby loss in weight after 10 minutes at 160 C. of a sample impregnatedsheet. As indicated, a so impregnated sheet member generally containsfrom about to 40 weight percent of solids derived from said firstcomposition.

To make a laminate of the invention from such an impregnated cellulosicsubstrate, the substrate is advanced to an extent such that it has aflow of from about 3 to 20 percent (preferably from about 5 to 15percent). To so advance a sheet member to such a flow it is convenientto heat in air such an intermediate sheet to temperatures in the rangeof from about 30 to 180 C. for a time sufficient to advance same to theso-desired extent. It will be appreciated that such an advancement canbe conveniently accomplished while residual volatile materials are beingremoved in a drying operation after impregnation, as indicated above.

Intermediate sheet-like members of this invention, whether advanced tothe extent indicated or not, are generally at least about 4 mils thickand can be as thick as 20 mils, though thicknesses not more than aboutmils are preferred.

The density of an individual impregnated sheet-like product isrelatively unimportant since the laminate, as described below, is formedunder heat and pressure conditions which generally solidify allcomponents together into an integral, solid, non-porous, thermoset mass.

To make a laminate construction from an impregnatedv sheet member asdescribed above, one forms at least one such sheet member (preferablyadvanced as described above) into a layered configuration which is atleast two layers thick with adjoining layers being substantially inface-to-face engagement. As those skilled in the art will appreciate, anindividual laminate construction of the invention can comprise a seriesof similar such intermediate members depending upon properties desiredin the product laminate.

Such a layered configuration is then subjected to pressure in the rangeof from about 50 to 200 p.s.i while maintaining temperatures in therange of from about 120 to 180 C. for a time sufiicient to substantiallycompletely thermoset the composite and thereby produce a desiredlaminate. Preferably the laminate is pressed at 140 to 160 C. at 500 to1500 p.s.i. for about to 60 minutes. It is preferred but not necessaryto use sheet members of this invention as the sole components forlaminates of this invention.

EMBODIMENTS The following additional examples are set forth toillustrate more clearly the principles and practices of this inventionto one skilled in the art, and they are not intended to be restrictivebut merely to be illustrative of the invention herein contained. Unlessotherwise stated herein, all parts and percentages are on a weightbasis.

The following additional examples are set forth to illustrate moreclearly the principles and practices of this invention to one skilled inthe art, and they are not intended to be restrictive but merely to beillustrative of the invention herein contained. Unless otherwise statedherein, all parts and percentages are on a weight basis.

Examples of liquid treating compositions (termed varnishes herein)suitable for use in making impregnated sheet members of this inventionare prepared as follows: The substituted phenol-formaldehyde resoleresin produced as described and employed in each varnish described has aformaldehyde to phenol ratio of from about 0.9 to 1.5. Each is producedby reacting in the presence of an organic basic catalyst under liquidaqueous phase conditions a substituted phenol mixture with formaldehyde.Each is substantially water insoluble, but has 21. methanol solubilitysuch that a 60 weight percent solution thereof can be prepared inmethanol, Each such methanol solution characteristically has a viscosityin the range from about 50 to 500 centipoises. Each resin has a freeformaldehyde content which is less than about 5 weight percent.

Examples of substituted phenols made with one preferred starting codimermixture used in this invention and resoles made therefrom are givenbelow.

EXAMPLE A To a stirred reaction vessel parts of phenol and 0.5 partconcentrated sulfuric acid are charged and the resulting mixture isheated to C. Then 25 parts of a diene codimer compound mixture availablecommercially under the trade designation Discyclopentadiene Concentratefrom Monsanto Company and having a composition as described above inTable I are added to this phenol mixture over a thirty minute period,keeping the temperature between 125 and C. After the addition, themixture temperature is held at 125 to 135 C. for fifteen minutes. Theproduct is a substituted phenol mixture.

EXAMPLES B TO 1' Using the procedure and raw materials described inExample A, additional substituted phenol mixtures are prepared, as shownin Table VI below:

Examples of phenolic resole resin varnishes of this invention are givenbelow.

EXAMPLE 1' To the substituted phenol mixture made in Example A is added(per 100 parts of phenol) 2 parts triethylamine, 2 partshexamethylenetetramine and 83 parts of 50% Formalin. This mixture isheated to a 100 C. reflux for 55 minutes, then cooled to 50 C. toproduce a resole resin which is then dehydrated to 60 C. and 26 inchesHg. When this temperature is reached, 80 parts methanol are added andthe solution cooled. The product varnish is clear and thermally cures togive a clear film on a heated steel surface. The varnish has 60.3%solids and an Ostwald viscosity of 98 centipoises.

EXAMPLE 2 To the substituted phenol mixture made in Example D' is added(per 100 parts of phenol) 2 parts of triethylamine, 3 parts ofhexamethylenetetramine and 60 parts of 50% Formalin. The mixture isheated to a 100 C. reflux for 50 minutes, then cooled to 5 0 C. toproduce a resole resin which is then dehydrated to 60 C. and 27 inchesHg. When this temperature is reached 70 parts methanol and 10 partsmethyl ethyl ketone are added. A clear varnish is obtained whichthermally cures to give a clear film on a heated steel surface.

EXAMPLES 3 TO 9' Examples of other varnishes of this invention aresummarized in Table VII. Preparation procedure for each is as given inExampleI'. In each instance, a clear varnish is obtained which thermallycures to give a clear film.

EXAMPLE To a stirred reaction vessel 100 parts of phenol and 0.5 partconcentrated sulfuric acid are charged and the resulting mixture isheated to about 125 C. Then 30 parts of a diene codimer mixture areadded to the phenol mixture over a thirty minute period, keeping thetemperature between 125 and 135 C. This diene codimer compound mixturecomprises, when in a form substantially free of other materials whereinthe sum of all component compounds of any given such mixture equalssubstantially 100 weight percent, about 70 weight percentdicyclopentadiene, about 28 weight percent of codimers ofcyclopentadiene with butadiene and isoprene (50/50) and about 2 weightpercent of 50/50 l-pentene and l-hexene mix. This diene codimer mixtureadditionally contains about 10 weight percent toluene as an inertiluent. After the addition, the product mixture is held at 125 to 135 C.for about fifteen minutes.

To this substituted phenol product mixture is then added (per 100 partsof phenol) 2 parts triethylamine, 2 parts by weighthexamethylenetetramine and 83 parts by weight of 50% formalin. Thismixture is heated to a 100 C. reflux for about 55 minutes, then cooledto 50 C. to produce a resole resin which is then dehydrated under vacuumto 60 C. and 26 inches Hg. When this temperature is reached, 80 partsmethanol are added and the solution cooled. The varnish product soproduced is clear and thermally cures to give a clear film on a heatedsteel surface.

EXAMPLE 11' The procedure of Example 10' is repeated except that herethe diene codimer compound mixture comprises, when in a formsubstantially free of other materials wherein the sum of all componentcompounds of any given such mixture equals substantially 100 weightpercent, about 90 weight percent of dicyclopentadiene, about 8 weightpercent of codimers of cyclopentadiene with butadiene andisoprene'(50/50), and about 2 weight percent of 50/50 l-pentene andl-hexene mix.

This diene codimer mixture additionally contains about 10 weight percenttoluene as an inert diluent. This varnish product so produced is clearand thermally cures to give a clear film on a heated steel surface.

EXAMPLE 12' The procedure of Example 10' is repeated except that herethe diene codimer mixture comprises, when in a form substantially freeof other materials wherein the sum of all component compounds of anygiven such mixture equals substantially 100 weight percent, about 80weight percent dicyclopentadiene, about 5 weight percent of codimers ofcyclopentadiene with butadiene and isoprene (50/50), and about 15 weightpercent of 50/ 50 l-pentene and l-hexene mix. This diene codimer mixtureadditionally contains about 10 weight percent toluene as an inertdiluent. The varnish product so produced is clear and thermally cures togive a clear film on a heated steel surface.

EXAMPLE A" To a stirred reaction vessel 100 parts of phenol and 0.5 partconcentrated sulfuric acid are charged and the resulting mixture isheated to 125 C. Then parts of a diene codimer mixture availablecommercially under the trade designation Resin Former P from the HessOil and Chemical Company and having a composition as described above inTable II are added to the phenol mixture over a thirty minute period,keeping the temperature between 125 and 135 C. After the addition, themixture is held at 125 to 135 C. for fifteen minutes. The product is asubstituted phenol mixture.

EXAMPLES B TO 1" Using the procedure and raw materials described inExample A", additional substituted phenol mixtures are prepared as shownon Table VIII below:

TABLE VIII Diene eodi- Post mer mixreaction Friedel-Craits ture, partsReaction holding Example catalyst, parts per 100 temperatempera- No. per100 phenol phenol ture, C. ture, O.

20 125 20 40 125 30 50 125 50 60 150 60 20 60 15 60 150 60 H AlOl -1.030 125 15 I BFQ etherate-0.5. 70 150 60 Examples of phenolic resoleresin varnishes of this invention are illustrated below.

EXAMPLE 1" To the substituted phenol mixture made in Example A" is added(per 100 parts of phenol) 2 parts triethylamine, 2 parts hexamethylenetetramine and 83 parts of 50% Formalin. This mixture is heated to a 100C. reflux for 55 minutes, then cooled to 50 C. to produce a resole resinwhich is then dehydrated to 60 C. and 26 inches Hg. When thistemperature is reached, parts methanol are added and the solutioncooled. The varnish product so produced is clear and thermally cures togive a clear film on a heated steel surface.

EXAMPLE 2" T0 the substituted phenol mixture made in Example D" is added(per parts of phenol) 2 parts of triethylamine, 3 parts ofhexamethylenetetramine and 60 parts of 50% Formalin. The mixture isheated to a 100 C. reflux for 50 minutes, then cooled to 50 C. toproduce a resole resin which is then dehydrated to 60 C. and 27 inchesHg. When this temperature is reached, 70 parts methanol and 10 partsmethyl ethyl ketone are added. A clear varnish product is thus obtainedwhich thermally cures to give a clear film on a heated steel surface.

TABLE 1X Resole prep- Substituted aration phenol, Ex. No.

Example No.

EXAMPLE 10" To a stirred reaction vessel 100 parts of phenol and 0.5part concentrated sulfuric acid are charged and the resulting mixture isheated to about C. Then 30 parts of a diene codimer mixture are added tothe phenol mixture over a thirty minute period, keeping the temperaturebetween 125 and 135 C. This diene codimer mixture comprises, when in aform substantially free of other materials wherein the sum of allcomponent compounds of any given such mixture equals substantially 100weight percent, about percent by weight of indene, about 70 percent byweight of dicyclopentadiene, about 5 percent by weight of codimers ofcyclopentadiene with butadiene and isoprene (50/ 50) and about 20% byweight styrene. This diene codimer mixture additionally contains aboutweight percent toluene as an inert diluent. After the addition, theproduct mixture is held at 125 to 135 C. for about fifteen minutes.

To this substituted phenol product mixture is then added (per 100 partsof phenol) 2 parts triethylarnine, 2 parts by weight hexamethylinetetramine and 83 parts by weight of 50% Formaline. This mixture isheated to a 100 C. reflux for about 55 minutes, then cooled to 50 C. toproduce a resole resin which is then dehydrated under vacuum to 60 C.and 26 inches Hg. When this temperature is reached, 80 parts methanolare added and the solution cooled. The varnish product so produced isclear and thermally cures to give a clear film on a heated steelsurface.

EXAMPLE 1 1" The procedure of Example 10" is repeated except that herethe diene codimer mixture comprises, when in a form substantially freeof other materials wherein the sum of all component compounds of anygiven such mixture equals substantially 100 weight percent, about 10percent by Weight of indene, about 50 percent by weight ofdicyclopentadiene, about 10 percent by weight of codimers ofcyclopentadiene with butadiene and isoprene (50/ 50) and about 30percent by Weight styrene. This diene codimer mixture additionallycontains about 10 weight percent toluene as an inert diluent. Thevarnish product so produced is clear and thermally cures to give a clearfilm on a heated steel surface.

EXAMPLE 12 The procedure of Example 10 is repeated except that here thediene codimer mixture comprises, when in a form substantially free ofother materials wherein the sum of all component compounds of any givensuch mixture equals substantially 100 weight percent, about 5 percent byweight indene, about 85 percent by weight dicyclopentadiene, about 5percent by weight of codimers of cyclopentadiene with butadiene andisoprene, (50/50), and about 5 percent by weight of styrene. This dienecodimer mixture additionally contains about 10 weight percent toluene asan inert diluent. The varnish product so produced is clear and thermallycures to give a clear film on a heated steel surface.

Examples of suitable substituted phenol mixtures made with anotherpreferred starting mixture used in this invention and resoles madetherefrom are given below:

EXAMPLE A" To a stirred reaction vessel 100 parts of phenol and 0.5 partconcentrated sulfuric acid are charged and the resulting mixture isheated to 125 C. Then 25 parts of a cyclopentadiene codimer compoundmixture available commercially from Eastman Chemical Company under thetrade designation Dicyclopentadiene and having a composition asdescribed in Table III above are added to the phenol mixture over athirty minute period, keeping the temperature between 125 and 135 C.After the addition, the mixture temperature is held at 125 to 135 C. forfifteen minutes. The product is a substituted phenol mixture.

EXAMPLES B' TO 1" Using the procedure and raw materials described inExample A' additional substituted phenol mixtures are prepared, as shownin Table X below:

Cyclo- Friedelpentadiene Post Crafts compound reaction catalyst,mixture, Reaction holding Example parts per parts per temperaperiod, No.phenol 100 phenol ture minutes Examples of phenolic resole resinvarnishes of this invention are illustrated below. The substitutedphenolformaldehyde resole resin produced as described and employed ineach varnish product has a formaldehyde to phenol ratio of from about0.9 to 1.5. Each is produced by reacting in the presence of an organicbasic catalyst under liquid aqueous phase conditions a substitutedphenol mixture with formaldehyde. Each is substantially water insoluble,but has a methanol solubility such that a 60 weight percent solutionthereof can be prepared in methanol. Each such methanol solutioncharacteristically has a viscosity in the range from about 50 to 500centipoises. Each resin has a free formaldehyde content which is lessthan about 5 weight percent. Each of the product varnishes is suitablefor use in impregnating cellulosic substrates.

EXAMPLE 1" To the substituted phenol mixture made in Example A' is added(per 100 parts of phenol) 2 parts triethylamine, 2 partshexamethylenetetramine and 83 parts of 50% Formalin. This mixture isheated to a 100 C. reflux for one hour, then cooled to 50 C. to producea resole resin which is then dehydrated to 70 C. and 26 inches Hg. Whenthis temperature is reached, 80 parts methanol are added and thesolution cooled. The product varnish is clear and thermally cures togive a clear film on a heated steel surface. The varnish has 61% solidsand an Ostwald viscosity of 123 centipoises.

EXAMPLE 2" EXAMPLE 3" TO 10" Examples of other varnishes of thisinvention are summarized in Table XI. Preparative procedures used are asshown in this table. In each instance, a clear varnish is obtainedwhichthermally cures to give a clear film.

TABLE XI Resole Substituted preparation Example phenol Ex. method, N o.No. x. N 0

Methylolation catalyst parts per 100 phenol 1 EXAMPLE 11'" To a stirredreaction vessel 100 parts of phenol and 0.5 part concentrated sulfuricacid are charged and the resulting mixture is heated to about 125 C.Then parts of a diene codimer mixture are added to the phenol mixtureover a thirty minute period, keeping the temperature between 125 and 135C. This diene codimer mixture is a cyclopentadiene codimer compoundmixture available commercially from Union Carbide Company under thetrade designation Dicyclopentadiene and having a composition asdescribed in Table 1 above. After the addition, the product mixture isheld at 125 to 135 C. for about fifteen minutes.

To this substituted phenol product mixture is then added (per 100 partsof phenol) 2 parts triethylamine, 2 parts by weighthexamethyline-tetramine and 83 parts by weight of Formalin. This mixtureis heated to a 100 C. reflux for about minutes, then cooled to 50 C. toproduce a resole resin which is then dehydrated under vacuum to C. and26 inches Hg. When this temperature is reached parts methanol are addedand the solution cooled. The varnish product so produced is clear andthermally cures to give a clear film on a heated steel surface.

EXAMPLE 12" The procedure of Example 11" is repeated except that herethe diene codimer mixture comprises, when in a form substantially freeof other materials wherein the sum of all component compounds of anygiven such mixture equals substantially weight percent, about 91 weightpercent dicyclopentadiene, about 5 weight percent of codimers ofcyclopentadiene with butadinene and isoprene (50/50), and about 4 weightpercent of a codimer oi cyclopentadiene with a methyl cyclopentadiene.This diene codimer mixture additionally contains about 10 weight percenttoluene as an inert diluent. The varnish product so produced is clearand thermally cures to give a clear film on a heated steel surface.Examples of impregnated cellulosic sheet members made with the resolevarnish of this invention are as follows:

EXAMPLES 13 TO 18 Preformed cellulosic substrate types are chosen asfollows:

Type 1Non-woven cotton linters paper, about 10 mils thick.

Type 2Non-woven cellulose fiber paper containing 12% of a syntheticfiber (polyester) about 10 mils thick. Both types have an ash contentless than about 0.9 Weight percent. Each such substrate type isimpregnated with a resole resin varnish. The impregnation procedure forimpregnating each above substrate is as follows: The cellulosic sheetsabout 10 in. sq. are each passed through a specified impregnatingsolution (varnish) diluted to a specified solids content, drawn throughthe nip region between a pair of squeeze rolls to remove excess resinand hung in an oven to dry at C. for about 320 minutes for a timesuflicient to also advance the resin but not gel it. The resin contentof each sheet is about 15 to 20 Weight percent. Thereafter eachimpregnated sheet is examined and it is observed that it is foldablewithout cracking and is porous. Thereafter the sheets are cured at 160C. for ten minutes. It is observed that each product sheet has goodtensile strength and flexibility characteristics. Each sheet also hasporosity characteristics making it useful as an oil filter. It is foundthat the sheets are stable in hot (above C. motor oil for indefiniteperiods of time.

Details concerning such impregnated cellulose sheets are shown in TableXII.

1 Total weight percent basis.

Examples of laminates made from the impregnated cellulosic sheets ofthis invention follow:

EXAMPLES 19 TO 28 Preformed cellulosic substrate types are chosen asfollows:

Type l-Non-woven cotton linters paper, about 10 mils thick.

Type 2Non-woven unbleached kraft paper about 7 mils thick.

Type 3Non-woven lX-CelllllOSe paper about 10 mils thick.

Type 4Non-woven bleached kraft paper about 15 mils thick.

Type 5-Woven cotton duck about 8 02. weight.

Type 6Woven linen cloth about 4 oz. weight.

A resole varnish is used to impregnate the above sheets of preformedcellulosic substrates having dimensions of about 9 X 12 inches and anash content under about 0.5 Weight percent using the impregnatingprocedure of Examples 13 to 19 to produce sheets having a resin contentof about 50-60 weight percent. Each impregnated sheet is heated in a 135C. oven for about 5 to 20 minutes until r it has a flow of about 4 to 15percent. Thereafter the sheets so impregnated with each varnish arestacked together in a deck and laminated together by placing theso-formed deck under pressure between opposing faces of about 1000 psi.using a temperature of about C.

for about 30 minutes. A laminate is thus produced in each instancehaving excellent tensile strength and flexibility characteristics.Except for laminate made from varnishes 8', 8", and 10" the laminateshave good electrical (dielectric constants and dissipation factors)properties. Details concerning such impregnated cellulose sheets areshown in Table XIII.

TABLE XIII Solution Prefromed Example Treating solids substrate ResinNumber N 0. Ex. No. content X type content 1 of Sheets 3' e0 1 58 s 3'e0 2 e2 10 3 e0 3 61 8 3' 60 4 e0 6 3' 60 5 55 4 3' 60 e 5e 5 2" e0 1 60s 3" so 1 62 s 3'" 60 1 59 s 6 e0 1 59 s 1 Weight percent basis.

The product impregnated substrates have good electrical and mechanicalproperties.

EXAMPLE 29 Using the impregnation procedure of Examples 19 to 28, thevarnish of Example 1' is impregnated into sheets of 10 mil cottonlinters paper and dried to give sheets having resin contents of about 50and about 60 weight percent respectively. A laminate of about 10 layersfrom the 50 weight percent resin impregnated sheets and a laminate ofabout 8 layers from the 60 weight percent resin impregnated sheets areeach made by laying up such respective sheets and curing for 30 minutesat 280 F. and 1000 psi. Excellent properties are obtained as shown inTable XIV.

17 EXAMPLE 30 Using the impregnation procedure of Examples 19 to 28, thevarnish of Example 1' is impregnated into sheets of 10 mil cottonlinters paper and dried to give 18 (1) the dicyclopentadiene nucleus (2)from 10 through 13 carbon atoms (3) as nuclear substituents from through3 methyl groups and sheets having resin content of about 50 and of about60 5 (B) from about 1 to 50 Weight percent of comweight percentrespectively. A laminate of about Pounds each molecule of Which is a cer layers from the 50 weight percent resin impregnated sheets of cyclopeWith at least Oflb acyclic and a laminate of about 8 layers from the 60weight perconjugated alkadiene having from 4 through 6 cent resinlmpregnated sheets are each made by laying carbon atoms per molecule.

up such respect1ve sheets and curing for minutes at 10 2. The product ofclaim 1 wherein said mixture of 280 F. and 1000 p.s.1. Excellentpropernes are obta1ned l diene dimers (same basis) comprises:

as shown 1n Table XIV. (A) from about 70 to 90 weight percent ofdicyclo- EXAMPLE 31 pentadiene Using the impregnation procedure ofExamples 19 to 5 (B g f 2 fifi i p g g q 28, the varnish of Example 2 isimpregnated into 10 mil poun S mo u e o 1S c liner 0 cotton linterspaper and dried to givg Sheets having a cyclopentadiene with at leastone acyclic conjugated resin content of about 60 percent. A laminateabout 8 alkadlene' havmg from 4 through 6 carbon atoms layers thick madefrom the 80 impregnated sheets is I moleculeeand cured for 30 minutes at320 F. and 1000 psi. Excellent 20 from about 2 to 15 g tp t cmproperties are obtained as shown in Table XIV. PoundS each molecule ofwh1ch 1S a cycllc aIld/Or TABLE XIV Water Dielectric constantDissipation factor Flexural strength,

absorption, at 10 e.p.s. at 10 c.p.s. p.s.1. Laminate example coiii e ri t A D24/23 D48/50 A D24/23 D48/50 MD XMD .042 .045 28 8133 it; :1 5.41 .039 .040 50 0.80 4.77 5.00 .044 .047 31,060 20,980 60 0. 55 4. 764.87 .038 .041 24,700 17,130 00 0. s1 4. 11 4. 24 4. 00 .032 034 080What is claimed is: an acyclic conjugated alkadiene having 5 or 6carbon 1. A laminate comprising: atoms per molecule. I

(a) a plurality of integral cellulosic substrate members 3. The productof claim 1 wherem sa d mixture of in sheet-like form arranged face toface in a layered y p i n im m b i c mprises: configuration, (A) fromabout 1.5 to 10 welght percent of com- (b) each such substrate memberbeing impregnated pounds each molecule of which has:

with a thermoset substituted phenol-formaldehyde (l) the indene nucleusresole resin, (2) from 9 through 13 carbon atoms (c) each such memberbeing bonded substantially in (3) as nuclear substltuents from 0 through4 face-to-face engagement to its adjacent member by 45 methyl groups hth r i (B) from about to 70 weight perecent of com- (d) such resincomprising from about 30 to 70 parts pounds each molecule of which has:

by weight of said laminate with the balance up to (l) thed1cyclopentad1ene nucleus 100 weight percent of any given such laminatebeing (2) from about 10 through 13 carbon atoms substantially suchmembers, 50 (3) as nuclear substit-uents from 0 through 3 (e) saidresole resin being characterized by: methylgroups,

(1) having aformaldehyde to phenol mol ratio of from about 4 t0 10Weight P t of Comfl-om about 03 to 10 pounds each molecule of which is aco ilmer of (2) being produced by reacting under aqueous cyclopentadlbneb at least 0116 abycllc t liquid phase conditions formaldehyde and agated alkadlene havlng from 4 through 6 Carbon substituted phenolmixture in the presence of 21301115 P molecule, and a basic 6 at al yst(D from about 4 to 30 weight percent of compounds (3) beingsubstantially insoluble in water but each molecule of wh1ch 11351 havinga viscosity in methanol solution at (1) a Phenyl group substlt'uted y avlnylldenb weight percent solids concentration of not greater 60 p, thanabout 5000 centipoises, and fIOm 8 h ug 1 carb n atoms (4) having a freeformaldehyde content which (3) as substltuents from 0 b 31 p is lessthan about 5 Weight percent, selected from the class cons1st1ng ofmethyl and (f) said substituted phenol mixture having been preethY paredby reacting phenol under Friedel-Crafts con- 5 4. The product of cla1m 1wherem sa d mixture of ditions with from about 10 to 100 parts by weightcyclopentadiene dimers (same basis) compnses: for each 100 parts byweight of said phenol of a (A) from about 92 to 96 welght percent ofdicyclomixture of cyclopentadiene dimers, pentadiene,

(g) said mixture of cyclopentadiene dimers compris- (B") from about 3 toweight percent of compounds ing (when in a form substantially free ofother maeach molecule of wh1ch 1s a codimer of cyclopentaterials whereinthe sum of all component compounds diene wlth at least one acyclic conugated alkadiene in any given such mixture equals substantially 100having from 4 through 6 carbon atoms per molecule, weight percent) and(A) from about 50 to 99 weight percent of com- (C"') from about 1 to 4we1ght percent of compounds pounds each molecule of which has: eachmolecule of which is a codimer of cyclopenta- 19 d ene with amethylcyclopentadieneg provided that the sum of (A") and (C") in anygiven such cyclopentadiene dimer mixture is always at least about 95weight percent thereof (same basis). 5. The laminate of claim 1 whereineach substrate member has an ash content under 0.5 weight percent.

6. A laminate of claim 1 wherein each substrate member ranges from about3 to 30 mils.

7. A laminate of claim 6 wherein each substrate member is under 10 milsin thickness.

References Cited UNITED STATES PATENTS 1/1947 Rhodes 16l259 3/1958Christenson et a1. l6l264 US. Cl. X.R.

